Process for the size reduction of expanded plastics

ABSTRACT

A PROCESS FOR THE SIZE REDUCTION OF EXPANDED PLASTICS, COMPRISING PRELIMINARY SIZE OREDUCTION OF EXPANDED PLASTICS BLOCKS BY SHEARING ACTION BETWEEN ROLLERS ARMED WITH SHEAR BLADES AND STATIONARY BLADES AND FURTHER SIZE REDUCTION BY CONTINUED SHEARING ACTION.

United States Patent [72] Inventors Leo Unterstenhoefer llimburgerhofPfalz; Wilhelm Krieger, Ludwigshafen (Rhine), Germany [21] Appl. No.759,563

[22] Filed Sept. 13, 1968 [45] Patented June 28, 1971 [73] AssigneeBadische Anilin & Soda Fabrik Aktiengesellschaft, Ludwigshafen (Rhine),Germany [32] Priority Sept. 15, 1967 [33] Germany [54] PROCESS FOR THESIZE REDUCTION OF EXPANDED PLASTICS 2 Claims, 2 Drawing Figs.

[52] US. Cl 241/29 [51] Int. Cl ..B02c13/44, B02c 18/06 [50] FieldofSearch 241/3, 27, 29, 154, 158, 235 (Cursory), 239 (Cursory), 243(Cursory), 25

[56] References Cited UNlTED STATES PATENTS 1,312,717 8/1919 Zoeller241/158 1,501,282 7/1924 Kost 241/158X 2,624,514 1/1953 Wi1housky....241/3 3,217,988 11/1965 Lightfoot 241/154X Primary Examiner- Donald G.Kelly Attorney-Johnston, Root, O'Keeffe, Keil, Thompson and ShurtleffABSTRACT: A process for the size reduction of expanded plastics,comprising preliminary size reduction of expanded plastics blocks byshearing action between rollers armed with shear blades and stationaryblades and further size reduction by continued shearing action.

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PATENTED JUN28|97I 3587.981

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IN vulv'l'oms: LEO UNTERSTENHOEFER WILHELM KRIEGER g ww ww ATT'YSPROCESS FOR THE SIZE REDUCTION OF EXPANDED PLASTICS This inventionrelates to a process for the size reduction of aminoplastics in blockform.

Expanded aminoplastics, particularly expanded urea-formaldehydecondensation products, are widely used as insulating materials againstheat and cold. Moreover, in particulate form they are frequently mixedwith garden and agricultural soils because they improve the heatretaining properties of the soils, provide satisfactory aeration andpossess a certain water retentivity. Finally their ability to soak upoils makes them particularly useful for absorbing oil from oil-watermixtures, condensable oil vapors from gases or oily contaminants fromfloors and the like. This property is due to the structure of theexpanded material which consists ofa multitude of openpored cells whichhave a very pronounced capillary action.

It has been found that in many cases such expanded materials do notdevelop a sufficiently powerful action unless they are in a specificparticulate form. When added to soils, which may consist of clay, sandand peat, it is essential that the expanded material should be added inflocculent form, the average size of the flocks being between 2 and mm.to avoid impairing the water retentivity and volumetric yield of themixture of soil and expanded material. For the absorption of oilexpanded aminoplastics in flock form have proved to be particularlyuseful provided they contain little flock having diameters below about 1mm.

It is .technically nearly impossible to reduce expanded aminoplasticsmechanically to particles of uniform size by grinding, ripping orcutting. The brittleness of the expanded aminoplastics, particularly ofexpanded urea-formaldehyde condensation products, when subjected toconventional methods of size reduction, for instance in mills, inbeaters fitted with spiked rollers or in blower-type chopping machines,particularly when the throughputs are large, results in flock of veryunequal size or containing an excessively high proportion of lines. Thequality of comminution is usually checked by a screen analysis and theyield by weight of floccules that are within the desired range of sizesis determined as a proportion of the total weight of material that hasbeen comminuted.

The primary object of the present invention is the mechanical sizereduction of expanded aminoplastics to particles of uniform size withoutthe generation of an excessive portion of fines.

This object is achieved by a process for the size reduction of blocks ofexpanded aminoplastics, particularly urea-formaldehyde condensationproducts, in two or several consecutive zones of progressivecomminution, the proposed process comprising the following steps:

a. in a first stage the blocks are cut into strips at a shearing speedof 0.3 to 5 meters/second by a pair of rollers armed with shear teethand mounted for contrarotation about their respective longitudinal axes,said strips being forced aa. over a shear blade and through shearingcombs arranged below said blade, and

b. the fragmentsthus obtained, without being allowed to accumulate, fallinto a zone in which they are further comminuted in a second stage at ashearing speed of 2 to 17 meters/second, by a roller armed with shearteeth cooperating with a shearing comb, the possible throughput throughthe second zone being at least equal to the throughput through the firstzone to avoid any accumulation ofmaterial.

Apparatus for performing the proposed method comprises a. two parallelrollers which are mounted for contrarotation about their horizontallongitudinal axes and which convey the blocks of expanded material tothe center, each of said rollers being armed at intervals of arc ofbetween 70 and 150 mm. about their peripheries with radially projectingan possibly relief-ground shear teeth which are 20 to 40 mm. wide anddisposed helically around the roller peripheries,

aa. a shear blade extending parallel to the roller axes between therollers and, below said shear blade, shear combs of a first comminutionzone which may be adjustable to provide a desired depth of engagement,and

b. below the rollers of the first comminution zone a horizontallydisposed roller armed at intervals of arc of between 70 and mm. aboutits periphery with radially projecting shear teeth, 3 to 8 mm. wide,disposed in rows parallel to the roller axis and cooperating with ashearing comb through the gaps of which said shear teeth pass, the shearing comb possibly being adjustable to a desired depth of interengagementand being located vertically below the shear blade of the firstcomminution zone, the minimum lateral clearance between the shear teethand the shearing comb and the minimum clearance in depth between shearteeth and shearing comb in the two disintegration zones being between 3and 13 mm. and l and 7 mm. respectively.

The process and apparatus suitable for performing the process accordingto the invention will be hereinafter described in more detail withreference to the drawing.

From blocks of an expanded aminoplastics, preferably of aurea-formaldehyde condensation product, entering a casing 1 through anopening 9, the shear teeth 3 of a pair of contrarotating rollers 2 cutout strips which have cross-sectional dimensions between 2 and 10 cm.,and which are forced between the rollers across shear blades 4 andshearing combs 5 which cut the strips into shorter lengths. Withoutbeing allowed to accumulate these lengths fall into a second comminutionzone which the shear teeth 6 of a roller 7 force them through the gapsof a shearing comb 8 for a further reduction in size of the lengths ofexpanded plastics. Further comminuting zones may follows. Instead of oneroller the second or additional comminuting zones may contain acontrarotating pair of rollers. The flock is discharged by gravity andmay then fall on a conveyor belt. The shearing speed in the firstcomminution zone is 0.3 to 5 meters/second, and in the second 2 to 17meters/second. However, the possible throughput which is determined bythe speed of the rollers in each consecutive zone should be equal to orgreater than that through the preceding zone. Shearing speed isunderstood to be the peripheral speed of the centers of the shear teethduring rotation of the rollers. Throughput is understood to mean thequantity by volume per unit of time of the expanded plastics that is tobe comminuted and will usually be given in cub.m./h.

Since the liability to brittle fracture generally increases with risingbulk weight of the expanded aminoplastics and shattering more readilyoccurs when the shearing speed is too high, the shearing speed should berelated to the bulk weight of the expanded aminoplastics. For a bulkweight of about 15 kg./cub.m. of the expanded aminoplastics the shearingspeed in the first comminution zone should be 1 to 5 m./sec., preferablybetween 1 and 3 m./sec., and in the second comminution zone 5 to 17m./sec., preferably 8 to 13 m./sec., whereas for a bulk weight'of about30 kg./cub.m. the shearing speed in the first comminution zone should be0.3 to 2 m./sec., preferably 0.45 to 1.0 m./sec., and in the secondcomminution zone 2 to 10 m./sec., preferably 2.5 to 6 m./sec. Besidesthe bulk weight of the expanded plastics another factor which governsthe shearing speed that should be chosen for the second comminution zoneis the size of the fragments produced in the first shearing zone.According to the size of the flock that is desired this must bedetermined by trial and error. For example, if the size of the piecesobtained in the first comminution zone is of about 50 mm. diameter, thanthe diameter of the floccules obtained at the stated shearing speeds inthe second comminution zone will be between 2 and 15 mm.

FIG. 1 is a cross section of a preferred apparatus for performing theproposed process, FIG. 2 being a sectional side elevation of theapparatus. The preferably horizontal parallel contrarotating rollers 2of the first comminution zone, which convey the expanded plastics blocksentering the casing 1 through an opening 9 towards the casing center arearmed with possibly relief-ground radially projecting shear teeth 3 of awidth between 20 and 40 mm., preferably between 24 and 30 mm., disposedhelically around the periphery of the rollers at intervals of arebetween 70 and 150 mm., preferably between 80 and 100 mm., and in apreferred embodiment they are forwardly curved in the direction ofrotation. Naturally the shear teeth might also be disposed in rowsparallel to the roller axis. Centrally between and below these rollers ashear blade 4 extends parallel to the roller axes, the edge of the bladepointing upwards. Shearing combs of which the depth of engagement may beadjustable and through which the shear teeth 3 pass are disposedparallel to the roller axes. The minimum lateral clearance between theshear teeth and the shearing comb is preferably 3 to 13 mm., preferablybetween 4 and mm., and the minimum clearance in depth is preferably 1 to7 mm. and, more particularly, 2 to 6 mm. Vertically below the shearblade 4 is a horizontal shearing comb 8 which may likewise be adjustableto a desired depth of engagement, and through which the shear teeth 6,preferably having a width of 3 to 8 mm., and particularly between 4 and6 mm., ofa roller 7 of a second comminution zone pass. These shear teethare preferably disposed in rows parallel to the roller axis and spacedthe same distances of arc apart as in the first disintegration zone. Theminimum lateral clearance and the minimum clearance in depth between theshear teeth and the shearing comb are the same as those specified forthe first comminution zone.

The distance of are between the shear teeth is understood to be thelength of the are between lines parallel to the roller axes on theroller periphery containing neighboring teeth.

In the proposed process the expanded plastics is comminuted and conveyedthrough the machine without forming local accumulations and withoutrotary motion about their own axes being imparted to the fragments,since this will always lead to the formation of a considerableproportion of fines by abrasion. A major advantage of the proposedprocess resides in that even at high rates of throughput the quality ofcomminution will always be high, i.e. a flock size distribution within adesired range will be obtained.

EXAMPLE 1 Blocks of an expanded urea-formaldehyde condensation producthaving a bulk weight of 30 kg./cub.m. are cut into strips in a firstcomminution zone by rollers which are 500 mm. long and have a diameterof 267 mm., and which at intervals of arc of 80 mm. are provided ontheir peripheral surfaces with radially projecting relief-ground shearteeth 30 mm. wide and 50 mm. high disposed helically about the rollerperipheries, the strips being forced over a 1.5 mm. thick shear bladethrough shearing combs 50 mm. wide with gaps 50 mm. in depth andproviding a clearance in the depth of engagement between shear teeth andshearing comb of 6 mm., to be thereby further disintegrated. Thefragments thus obtained fall by gravity without accumulation of materialinto the second comminution zone which comprises a roller of500 mm.length and 250 mm. diameter armed at intervals of arc of 80 mm. withradially projecting shear teeth 6 mm. 'wide and 10 mm. high disposed inrows parallel to the roller axis and they are forced through a shearingcomb located vertically below the shear blade in the first zone andhaving a width of 14 mm. and gaps that are 10 mm. deep to provide aclearance in depth of engagement of2 mm. The minimum lateral clearancebetween the shear teeth and the shearing comb in the first comminutionzone is 10 mm., and in the second zone 4 mm. The speed of rotation inthe first comminution zone is 27 rpm. and in the second 240 rpm. Theshearing speeds are 0.52 m./sec. and 3.25 m./sec. respectively. A screenanalysis gives the following particle size distribution.

42.4 percent by weight having diameters between 10 and 15 43.5 percentby weight having diameters between 5 and 10 10.5 percent by weighthaving diameters between 2 and 5 mm. 3.6 percent by weight havingdiameters of less than 2 4.5 cub.m. of expanded plastics in block formare fed into the machine per hour and 8.5 cub./m. per hour of expandedplastics in flock form are obtained.

By comparison a conventional blower-type chopping machine produces anexpanded plastics flock which a screen analysis proves to have thefollowing particle size distribution:

39 percent by weight having diameters between 15 and 50 15 percent byweight having diameters between 5 and 10 16 percent by weight havingdiameters between 2 and 5 20 to 30 percent by weight having diameters ofless than 2 The numerical analysis clearly shows the less regular particle size distribution and the high proportion of fines. Similarlyunsatisfactory results as those obtained with a blower-type choppingmachine are also obtained when using spiked rollers and ripper beaters.

EXAMPLE 2 Blocks of an expanded ureaformaldehyde condensation producthaving a bulk weight of 1S kg./cub.m. are cut into strips in a firstcomminution zone by rollers which are 700 mm. long and have a diameterof 3 l 8 mm., and which at intervals of arc of mm. are armed on theirperipheral surfaces with radially projecting relief-ground shear teeth30 mm. wide and 50 mm. high, arcuately bent in the direction of rotationand disposed helically about the roller peripheries, and then comminutedby being forced over a 1.5 mm. thick shear blade through shearing combsthat are 50 mm. wide with 50 mm. deep gaps providing a clearance indepth between the shear teeth and the shearing comb of 6 mm. Thefragments thus obtained fall freely, without accumulating, into thesecond disintegration zone which comprises a roller 700 mm. long and ofa diameter of 428 mm., armed at intervals of arc of 100 mm. on itsperipheral surface with rows parallel to the roller axis of shear teeth6 mm. wide and 10 mm. high, and vertically below the shear blade of thefirst zone a shearing comb 14 mm. wide with 10 mm. deep gaps providing aclearance in depth of 2 mm. The minimum lateral clearance between theshear teeth and the shearing blade in the first comminution zone is 10mm., in the second zone 4 mm. The speed of rotation in the firstcomminution zone is 61 rpm. and in the second zone 540 rpm, the shearingspeeds being 1.33 m./sec. and 12.4 m./sec. respectively. The screenanalysis gives the following particle size distribution:

44.5 percent by weight having diameters between 10 and 15 41.5 percentby weight having diameters between 5 and 10 10.8 percent by weighthaving diameters between 2 and 5 3.2 percent by weight having diametersofless than 2 mm.

25 cub.meters of expanded plastics in block form are fed into themachine per hour and 51 cub.m./h.'of expanded plastics in flock form areobtained. A disintegrator comprising a spiked roller produces expandedplastics flocks which a screen analysis proves to have the followingparticle size distribution: I

5 percent by weight having diameters between 10 and 12 18 percent byweight having diameters between 5 and 10 37 percent by weight havingdiameters between 2 and 5 40 percent by weight having diameters oflessthan 2 mm.

We claim:

l. A process for the size reduction of blocks of expanded aminoplasticsin two or more zones of progressive comminution wherein:

a. in the first stage the blocks are cut into strips at a shearingsecond by a roller provided with shear teeth cooperating speed of 0.3 to5 meters per second by a pair of rollers ith a shearing comb, thepossible throughput through provided with shear teeth and mounted forcontrarotation the Second zone being at least equal to h throughputabout their respectively longitudinal axes, said strips through the fi tzone to avoid any accumulation f being forced 5 material aa. into ashear blade and through shearing combs below 2 A process as claimed inclaim I wherein the expanded said blade to form fragments, and Y b. thefragments thus obtained fall, without accumulating, i g an expandedurea'formaldehyde condensatron pro uet.

into a zone in which they are further comminuted in a second stage atthe shearing speed of 2 to 17 meters per

